The present invention relates to the general field of compressors and turbines of aeroengines (in particular for airplanes or helicopters). More precisely the invention relates to controlling inlet guide vanes (IGVs) of a gas turbine engine.
The actuators of the IGVs are used to control the position of the prerotation vanes situated upstream from the compressor stage(s) on helicopter turbine engines (see for example US 2014/0286745). The function of such an actuator consists in directing the flow of air entering the engine upstream from the compressor. Varying the angular position of the prerotation vanes makes it possible to optimize the overall performance of the engine (transients and specific consumption).
The function of controlling the inlet guide vanes is usually provided by a hydraulic actuator powered by the fuel circuit having its flow rate and pressures directly indexed to the speed of the gas generator. However, such an architecture presents numerous drawbacks.
Firstly, due to their reversibility, present-day hydraulic actuators do not have “position memory” or “fail freeze”, i.e. in the event of a failure they do not maintain the last controlled position. Secondly, those actuators are dimensioned for a wide range of pressures and flow rates, which, due to interactions with the fuel circuit, causes real disruption to the fuel metering system each time fuel drives the actuator. The working pressure difference varies greatly depending on the engine operating point (low delta P when idling and high delta P at high speed). In addition, that overdimensioning has a non-negligible impact on the weight of the engine and causes unnecessary heating of the fuel and indirectly draws unwanted power from the accessory gearbox. Finally, those actuators are controllable only when the engine is in operation, which is particularly detrimental in the context of certain daily maintenance operations, such as engine endoscope inspections where the vanes need to be moved without starting the engine, since that requires the use of an external hydraulic unit.
U.S. Pat. No. 7,096,657 discloses a control system for controlling inlet guide vanes by means of a electric actuator that is provided redundantly, which can be either a brushless DC motor or an induction or variable reluctance AC motor. However, the use of a brushless motor requires control electronics that are particularly complex and restrictive from a point of view of electromagnetic compatibility, and the powers involved are not sufficient under all flight conditions. Similarly, in the event of a short circuit on the variable reluctance motor or its control electronics, the braking torque generated by the short circuit is very low or even zero, which necessarily requires the use of an external electric brake (energize-to-release type brakes) to freeze the last controlled position. This information is essential in order to switch safely to a degraded mode of controlling the motor. For both of these two types of motor, the same applies in the event of a loss of power.
There is therefore currently a need to control inlet guide vanes by means of a new actuator that does not have the above-mentioned drawbacks.